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#Mon Aug 09 11:42:17 CEST 2010
Text__XGgT4KOaEd-WfYQ0GneCwQ_title=Mass distributions acting as lenses
Text__XGgT4KOaEd-WfYQ0GneCwQ_text=The action of a mass as a lens is partly comparable with a focussing optical lens. Depending on the constellation of the source, the lens, and the observer and depending on the form of the lens different patterns of lensed images arise. <p><p></p></p>If the source, the lense and the observer are situated on a straight line and if the lens is spherical then the image appears as a ring - the <i>Einstein Ring</i> (top). <p><p></p></p>For a non-spherical lens one typically gets the <i>Einstein Cross</i> (middle). <p></p>For more general lenses more complex images are formed, typically in the form of arcs and arclets (bottom). <p></p><p>One can directly calculate the mass distribution of the lens from the position and the distortion of the images.</p>